Conventionally, X-ray computed tomography (CT) apparatus collect projection data by irradiating a subject with X-rays and detecting the X-rays that have passed through the subject, and reconstruct an image from the collected projection data. In recent X-ray CT apparatus, the matrix size of image data to be reconstructed is generally, “512×512”. In such a case, for example, if the diameter of the field of view (FOV), which is an imaging region, is 50 cm (500 mm), the size of a single pixel is “about 1 mm (500/512=0.98 mm). If the diameter of the FOV is “25 cm (250 mm), the size of a single pixel is “about 0.5 mm (250/512=0.49 mm).
In the recent X-ray CT apparatus, the maximum resolution defined by the geometry of the system, such as the focal size and the opening width of a detector, is about “0.35 mm”. In other words, to achieve the maximum resolution of “0.35” by the matrix size of “512×512”, the FOV will be about 18 cm (0.35×512=179.2 mm). To put it differently, when the FOV is larger than “18 cm”, it is difficult to achieve the maximum resolution. Accordingly, to achieve the maximum resolution, zooming reconstruction is performed to reduce the FOV. For example, if the FOV is reconstructed into “10 cm”, the size of a single pixel will be “about 0.2 mm (100/512)”. Consequently, the maximum resolution can be achieved.
However, in the conventional technology described above, it has sometimes been difficult to observe the entire region to be observed with high resolution.